Strontium-82 has a half-life of about 25 days and decays by pure electron capture to the ground state of its 75-second daughter, rubidium-82. Rubidium-82 in turn decays by 95% positron emission and 5% electron capture to stable krypton-82 while exhibiting several prominent gamma rays. The availability of the long-lived parent, strontium-82, is of significant interest for biomedical studies because of its generation of the short-lived alkali metal activity. The useful shelf-life is determined by the activity of the strontium-82, while the short half-life of the rubidium-82 minimizes the radiation dose to the patient. With a suitable positron imaging device, rubidium-82 has considerable usage in medical applications where repeated, rapid, dynamic blood-flow information is needed, for example, in the investigation of coronary occlusions, cardiac output, arteriography, or tumor vascularity.
U.S. Pat. No. 3,957,945 describes the chemical isolation of strontium-82 from an irradiated molybdenum target by a multi-step process including dissolution of the target in a hydrogen peroxide solution, reaction of the solution with a base such as ammonium hydroxide to selectively precipitate and separate hydrous molybdenum oxides containing large amounts of Zr and Y, reaction of the remaining solution with a lead compound such as lead nitrate to form a strontium-82 containing solid lead molybdenate species, reaction of the strontium-82 containing lead molybdenate species with a mixture of dilute HCl and bis-(2-ethylhexyl) phosphoric acid in toluene whereby both an aqueous and an organic layer are formed, adjusting the pH of the aqueous layer to basic followed by subsequent reaction of the alkaline solution with hydrogen sulfide to selectively precipitate and separate lead sulfide, acidification of the remaining solution to selectively precipitate and separate molybdenum sulfide, adjusting the pH of the remaining solution to about 6.0 followed by passage through an ion exchange column containing hydrous zirconium oxide and collection of a strontium-82 solution.
U.S. Pat. No. 4,276,267 describes the chemical isolation of strontium isotopes from an irradiated molybdenum target by another multi-step process including dissolving the target in a hydrogen peroxide solution, passing the solution through a cation exchange column to separate cationic species from anionic and neutral species, forming anionic chlorocomplexed species, separating the anionic chlorocomplexed species from the solution by anionic exchange, adjusting the pH of the solution to from about 0 to about 1, extracting selected ions from the solution with an organophosphorus solvent whereby the strontium ions remain in the aqueous phase, adjusting the pH of the solution to greater than about 10, passing the solution through a chelating resin whereby the strontium ions are preferentially adsorbed, and eluting the chelating resin with dilute hydrochloric acid to remove the strontium ions.
Each of these previous processes involved the use of one or more organic solvents in an extraction stage for the selective separation of the strontium. Eliminating the need for these materials in the separation is environmentally desirable as any radioactive waste solution, i.e., mixed hazardous waste, can be minimized.
Accordingly, it is an object of this invention to provide an improved process for the recovery of strontium isotopes, i.e., strontium-82 and strontium-85 from irradiated molybdenum targets and for the recovery of other desirable radioisotopes, e.g., zirconium-88, rubidium-83, and yttrium-88, from the molybdenum targets.
It is a further object of this invention to provide an organic solvent-free process for recovery of strontium-82 and strontium-85.
It is a still further object of this invention to provide an organic solvent-free process for recovery of zirconium-88, rubidium-83, and yttrium-88.